How to get the Document object in Visual Studio extensions

GetVisualStudioDocument.cs

// The wrong way:
private GetVisualStudioDocument(SnapshotPoint triggerLocation)
{
  // Get the VisualStudioWorkspace service
  var componentModel = (IComponentModel)Package.GetGlobalService(typeof(SComponentModel));
  var workspace = componentModel.GetService<VisualStudioWorkspace>();

  // Retrieve the document associated with the trigger location
  var documentId = workspace.CurrentSolution.GetDocumentId(triggerLocation.Snapshot.TextBuffer.AsTextContainer());
  if (documentId == null) return CompletionContext.Empty;

  return (document == null) ? CompletionContext.Empty : workspace.CurrentSolution.GetDocument(documentId);
}